Flash floods are one of the most frequent natural disasters in Fujian Province, China, and they seriously threaten the safety of infrastructure, natural ecosystems, and human life. Thus, recognition of possible flash flood locations and exploitation of more precise flash flood susceptibility maps are crucial to appropriate flash flood management in Fujian. Based on this objective, in this study, we developed a new method of flash flood susceptibility assessment. First, we utilized double standards, including the Pearson correlation coefficient (PCC) and Geodetector to screen the assessment indicator. Second, in order to consider the weight of each classification of indicator and the weights of the indicators simultaneously, we used the ensemble model of the certainty factor (CF) and logistic regression (LR) to establish a frame for the flash flood susceptibility assessment. Ultimately, we used this ensemble model (CF-LR), the standalone CF model, and the standalone LR model to prepare flash flood susceptibility maps for Fujian Province and compared their prediction performance. The results revealed the following. (1) Land use, topographic relief, and 24 h precipitation (H24_100) within a 100-year return period were the three main factors causing flash floods in Fujian Province. (2) The area under the curve (AUC) results showed that the CF-LR model had the best precision in terms of both the success rate (0.860) and the prediction rate (0.882). (3) The assessment results of all three models showed that between 22.27% and 29.35% of the study area have high and very high susceptibility levels, and these areas are mainly located in the east, south, and southeast coastal areas, and the north and west low mountain areas. The results of this study provide a scientific basis and support for flash flood prevention in Fujian Province. The proposed susceptibility assessment framework may also be helpful for other natural disaster susceptibility analyses.

Flash Flood Susceptibility Assessment Based on Geodetector, Certainty Factor, and Logistic Regression Analyses in Fujian Province, China

Old forests are an important component in sacred sites, yet they are at risk of growth decline from ongoing global warming and increased human activities. Growth decline, characterized by chronic loss of tree vigor, is not a recent phenomenon. Knowledge of past occurrence of declines is useful for preparing conservation plans because it helps understand if present day forests are outside the natural range of variation in tree health. We report a dendroecological study of growth decline events in the past two centuries at two sacred sites, Hengshan and Wutaishan, in Shanxi province of northern China. Tree rings collected at both sites show distinct periods of declining growth evident as narrow rings. These occurred in the 1830s in both sites, in the 1920s in Wutaishan and in the 2000s in Hengshan. By comparing the pattern of grow declines at the two sites, we hypothesize that resistance of tree growth to external disturbances is forest size dependent, and increased human activity might be a factor additional to climatic droughts in causing the recent strong growth decline at Hengshan Park. Despite these past declines, the forests at both sites have high resilience to disturbances as evidenced by the ability of trees to recover their growth rates to levels comparable to the pre-decline period. Managers should consider reducing fragmentation and restoring natural habitat of old forests, especially in areas on dry sites.

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History of Tree Growth Declines Recorded in Old Trees at Two Sacred Sites in Northern China.

IBIS (Integrated Biosphere Simulator) model is an ecosystem process model, which represents the research direction of a global carbon cycle simulation. Based on the existing research achievements, the regional ecological carbon sink potential is simulated from point to surface with a long time serie of meteorological data (1954-2010), data on different ecosystem vegetation types, soil texture data, terrain data and remote sensing data. The results are listed as follows: there is no significant variation of potential carbon sink of Shenzhen vegetation over the past 30 years, carbon sequestration caapcity ranges within 43.52-55.82×104 Mg C/a, and the potential carbon sink intensity value within 0-624 C/m2/a. Precipitation is a main factor which influnces the ecosystem carbon sink intensity in Shenzhen City. The carbon sink intensity of ecosystem is increased with more annual precipitation.

IBIS Model-Based Simulation Study on Variation of Ecological Carbon Sink Potential in Shenzhen City

Research on Chongqing Mountain Flood Disaster Risk Assessment System Based on AHP-GIS

This paper is to propose a method of ecological carbon sink regionalization in the view of GHG (greenhouse gas) emission reduction, which could provide scientific theory basis for development and utilization of urban land resources, ecological environment construction, biodiversity conservation, the industry layout and formulation of the regional sustainable development strategy. Based on the existing researches foundation, this study takes Shenzhen as a typical case to put forward a method for carbon sink regionalization of urban land use with further quantitative evaluation of ecosystem carbon storage (density), carbon sources/sinks function and carbon sink potential of Shenzhen city. The results show that: Shenzhen ecological carbon sink is regionalized into six categories 55 regions, including 15 intensive carbon sink regions, 17 medium carbon sink regions, 10 weak carbon sink regions, 4 carbon neutral regions, 5 medium carbon source regions and 4 intensive carbon source regions.

Study on Ecological Carbon Sink Regionalization of Land Use in Shenzhen City

The change of soil carbon pool has a significant impact on the global greenhouse effect and carbon cycle.Urban soil is an important part of the global carbon cycle.The impact of urbanization on soil organic carbon pool needs to be examined.Based on the field investigation and samples in Shenzhen City,soil organic carbon content,density and distribution were analyzed.The soil depth of samples from different land use types were 0～10,11～20 and 21～30 cm.The results are as follows.(1) The average soil organic carbon content was 0.72～40.52 g·kg~(-1),and average soil organic carbon density was 0.27～13.36 kg·m~(-2) in the soil depth of 0～30 cm.(2) The soil organic carbon content and density decreased with the increase of soil depth.In the soil depth of 0～10 cm,the average soil organic carbon content ranged between 1.56 to 71.88 g·kg~(-1),and the average organic carbon density ranged between 0.18 to 7.05 kg·m.~(-2)In the soil depth of 11～20 cm,the average soil organic carbon content ranged between 0.59 to 36.79 g·kg~(-1),and the average organic carbon density ranged between 0.09 to 4.5 kg·m~(-2).In the soil depth of 21～30 cm,the average soil organic carbon content ranged between 0 to 12.90 g·kg~(-1),and the average organic carbon density ranged between 0 to 1.78 kg·m~(-2).(3) The soil organic carbon content and density in forest land decreased with increasing altitude,and those in urban construction land and unused land were very low.(4) The land use change could affect the storage and distribution of soil organic carbon.

Content and density of soil organic carbon under different land use types in Shenzhen

For the prevention and treatment of flash flood disasters,the zoning of risk based on the master of their regional differentiation laws is an important link to scientifically analyze the disaster factors of the flood disasters and take appropriate preventive measures. Using 12 factors including multi-year averaged rainfall,soil type,slope,elevation,length of the longest convergence route,gradient of the longest convergence route,roughness,steady infiltration rate,population density,per unit area GDP,land use and vegetation coverage,and with a combination of AHP and Delphi methods adopted to determine the weights,the spatial overlay analysis was performed to complete flash flood hazard assessment map,vulnerability map and flood disaster risk zoning map at upper reaches of the Minjiang River. The maps were integrated with the disaster data in 1985-2013 to analyze and compare the flood disaster risk zoning and the actual disaster occurrence situations,so as to provide decision-making support for land use planning of different risk zones as well as the risk information to habitants in the disaster vulnerable zones.

Zhang Linbo

Papers

Content and density of soil organic carbon under different land use types in Shenzhen

GIS-based Risk Zoning of Flood Disasters in Upstream of the Minjiang River

The changes in ecosystem functions in Hengshan Scenic Spot Area from 2000 to 2010.